The goal of this research is to determine the axonal connections of certain neurons in the lower auditory pathway of the cat. Previous work has defined some of the basic organizational features of the afferent and efferent projections of the cochlear nucleus, including 1) the topographical representation of the cochlea within each of its subdivisions, 2) the binaural convergence of its projections onto various cell groups of the superior olivary complex, 3) the separate origins and terminations of ascending pathways from its major subdivisios and 4) the dual origins and terminations of the olivosochlear bundle, but significant gaps in our knowledge still exist. Accordingly, experiments are proposed which address specific connectional issues, utilizing, in different simultaneous combinations, a number of recent refinements in neuroanatomical methodology, including among others 1) the method of anterograde transport of 3H-labelled protein, 2) retrograde transport of horse-radish peroxidase (HRP), both the native and the histochemically inactive 3H apo-enzyme, 3) electrophysiological identification of the injection sites, and 4) intracellular injection of HRP into selected neurons. Among the specific experiments described here are ones aimed at determining the extent and origin of afferent innervation to the cochlear nucleus1) from the small unmyelinated neurons of the spiral ganglion (Type II ganglion cells), 2) from the two types of neurons the axons of which comprise the olivocochlear bundle, and 3) from the other periolivary and trapezoidal cell groups. In addition, it is proposed to test for the existence of reciprocal connections between small regions of the cochlear nucleus and its target cell groups along the auditory pathway and to establish the identify of the cells in the cochlear nucleus which innervate specific sites here.